Here is a question for you to ponder over. Most B&W developers contain Hydroquinone with either Metol or Phenidone or a Phenidone derivative. Both Metol and Phenidone are super-additive with Hydroquinone, so why add both of them in the same developer formula?

Keith Tapscott. wrote:Here is a question for you to ponder over. Most B&W developers contain Hydroquinone with either Metol or Phenidone or a Phenidone derivative. Both Metol and Phenidone are super-additive with Hydroquinone, so why add both of them in the same developer formula?

My understanding is (and someone will correct me if I'm wrong!!) but at a suitably low pH the hydroquinone doesn't do much except regenerate the metol or phenidone. If the carbonate is dilute enough the pH won't be high enough for the HQ do do any actual developing of itself.
Murray

Murray Kelly wrote:My understanding is (and someone will correct me if I'm wrong!!) but at a suitably low pH the hydroquinone doesn't do much except regenerate the metol or phenidone. If the carbonate is dilute enough the pH won't be high enough for the HQ do do any actual developing of itself.
Murray

As far as I know Murray, you are correct that the function of hydroquinone in a low to moderate pH developer, is to help regenerate metol or phenidone, although metol will work and keep fairly well as the sole developing agent, unlike phenidone, which is very short lived.
An example of the latter being the P.O.T.A formula originally used to tame very high contrast subjects.

A higher pH is needed for hydroquinone to work as a reducing agent in developers such as the Kodak D-8 formula.

Guys,
you are mis-informed about the relationship of the accelerators, Metol & Phenidone, and HQ. In the development process, Metol forms a salt with HQ and becomes ineffective. P acts as a catylist with the HQ to develop the exposed silver and then " searches for the next free HQ molecule", to continue the process until there is no more available HQ. This is the explanation of why MQ developers run "right up to the edge of the cliff and drop in the ocean." PQ developers " gradually slide into the ocean." The real differences and advantages of PQ over MQ are P is about 25 times more active than M, P is much less allergenic than M, P is much more resistant to high temperature (therefore we use it in machine process developers), P can be easily replenished, changing dilutition of a PQ developer will change contrast, and each form of P will change the standard curve to increase number of steps over M.
The advantage of a developer combining both is "bolstered syntax".

Lowell Huff wrote:Guys,
you are mis-informed about the relationship of the accelerators, Metol & Phenidone, and HQ. In the development process, Metol forms a salt with HQ and becomes ineffective. P acts as a catylist with the HQ to develop the exposed silver and then " searches for the next free HQ molecule", to continue the process until there is no more available HQ. This is the explanation of why MQ developers run "right up to the edge of the cliff and drop in the ocean." PQ developers " gradually slide into the ocean." The real differences and advantages of PQ over MQ are P is about 25 times more active than M, P is much less allergenic than M, P is much more resistant to high temperature (therefore we use it in machine process developers), P can be easily replenished, changing dilutition of a PQ developer will change contrast, and each form of P will change the standard curve to increase number of steps over M.
The advantage of a developer combining both is "bolstered syntax".

I do know that Geoffrey Crawley uses both phenidone and metol in many of his 'FX' formulas. There are perhaps reasons that are not always clear why a given combination will work 'better' than another; it just 'does'. It's all trial and error.

I cannot attribute any advantage to FX formulas using both P & M, other than marketing differentiation. Just as with the proclaimed "advantage" of "alkaline fixer over acid fixer", it cannot be supported with science. It is only OPINION.

Lowell Huff wrote:I cannot attribute any advantage to FX formulas using both P & M, other than marketing differentiation. Just as with the proclaimed "advantage" of "alkaline fixer over acid fixer", it cannot be supported with science. It is only OPINION.

Well these are published free formulas, so they're not making him any money...they're just formulas he came up with, so there's no reason to suppose that they are more complicated than necessary. He has developed these formulas after lots of research into improving acutance while maintaining fine grain and good tonal qualities. They are very good formulas, and I have tried several of them. If he thinks that PMQ formulas are better I'm sure he has his reasons. Some of his are PQ only, some have glycin also.

I didn't say they were bad formulas. I meant that they would not produce a,scientically measured, difference from other PQ formulas of the "modern" age of chemical formulas. You know, comparing apples to apples.

Lowell Huff wrote:Guys,
you are mis-informed about the relationship of the accelerators, Metol & Phenidone, and HQ. In the development process, Metol forms a salt with HQ and becomes ineffective. P acts as a catylist with the HQ to develop the exposed silver and then " searches for the next free HQ molecule", to continue the process until there is no more available HQ. This is the explanation of why MQ developers run "right up to the edge of the cliff and drop in the ocean." PQ developers " gradually slide into the ocean." The real differences and advantages of PQ over MQ are P is about 25 times more active than M, P is much less allergenic than M, P is much more resistant to high temperature (therefore we use it in machine process developers), P can be easily replenished, changing dilutition of a PQ developer will change contrast, and each form of P will change the standard curve to increase number of steps over M.
The advantage of a developer combining both is "bolstered syntax".

Lowell, I acknowledge that P.Q formulae are the most commonly available developers these days and for good reasons.
My comment for Phenidone having poor keeping properties, was for formulae where it is the only reducing agent, hence my mention of the P.O.T.A. formula which is 30 grams of anhydrous sodium sulphite and 1.5 grams of Phenidone dissolved in a litre of water (no Q or restrainer included).

P with Q is very efficient with very good keeping properties in stock-solutions.
P alone does not keep as well as M in single developing agent formulae, like D-23 or D-25. These are developers of simple formulae.

Kieth, Phenidone, by itself, is a very poor, slow speed developing agent, as documented by Grant Haist. The sodium sulfite in that formula is there as a silver solvent first, then an oxygen scavenger, to protect the P. When P or M are combined with HQ they then become what is described as a "superadditive" compound and multiply geometrically the combined effect, hense continous tone development.

Lowell Huff wrote:Kieth, Phenidone, by itself, is a very poor, slow speed developing agent, as documented by Grant Haist. The sodium sulfite in that formula is there as a silver solvent first, then an oxygen scavenger, to protect the P. When P or M are combined with HQ they then become what is described as a "superadditive" compound and multiply geometrically the combined effect, hense continous tone development.

In the last few months, I have tried Ilford DDX and Tetenal Ultrafin-Plus which are modern P.Q (Dimezone-S) developers and both are very good products.
Ultrafin-Plus should not be confused with the Ultrafin Liquid I asked about in the 1st post of this thread. Both are recommended to be diluted 1+4 as standard.

Although they are both good developers, they cost considerably more than those supplied in powder-form and the cost of shipping is also higher than the powders.
Liquids are more convenient than dry powders of course.

Lowell Huff wrote:Keith is there a question? What would you like me to clarify?

Yes Lowell, "in which way do you consider certain types of liquid developers will perform better than those sold in powder form like the old D-76/ID-11 standards and newer formulae like Microphen and Xtol, other than the convenience of them being sold as liquid concentrates?"

Almost all powder formulas are pre 1920 in origin. As powders they are are not as sophisticated as modern liquid formulas. In pre 1920, Scientists did not have the advantage of all the research into photography that was done in the following sixty years. The pre 1920 formulas were designed for those same emulsions. How many of those emulsions remain today? While those formulas will develop today's emulsions, their lack of sophistication will not "OPTIMIZE" the capability of todays' films and papers. The discussion on their economy of shipping and storage issues does not belong in a discussion of image quality; but i can address it if you wish, in a later "Fataw".
Microphen, uses Phenidone A instead of Metol as the "superadditive", which, in my estimation, makes it an improvement over the older powder formulas. It does not contain any anti fogs or anti cals.
XTOL's claim to fame is that it does not contain HQ as the developing agent. So what? It is a low to medium contrast film developer with all the inherent, well documented problems of mixing two different bags of powder into a liquid. Without HQ it is less likely to oxidize during periods of non use. It can be replenished and can be used as manual or in a machine processor. It is clearly superior to the other developers in this discussion.
If you would like me to compare these chemicals to Clayton's, I can do that. If you did not know, Ilford chemicals are manufactured by Tetnal and Kodak chemicals are manufactured by Champion Chemical.
CLAYTON CHEMICALS are made by CLAYTON CHEMICAL.